In distributed processing systems where multiple separated processor cards communicate with each other, the cards must be aware of each other and must know how to communicate with each other at the link level. In one distributed processing system marketed by the assignee of the present application as the Eagle® STP Platform, the process by which processor cards discover the presence of other cards connected to a common bus is referred to as alignment. According to the alignment process, each card in the distributed processing system exchanges messages with other cards in the system to determine the presence of every other card. Once the alignment message exchange is complete, the cards can communicate with each other.
FIG. 1 is a block diagram of a conventional signal transfer point in which alignment may be performed. In FIG. 1, signal transfer point 100 includes a plurality of link interface modules 102, a data communications module (DCM) 104, database services module (DSM) 106, and maintenance and administration subsystem processors (MASPs) 108. Modules 102, 104, 106, and 108 are connected by a dual ring, counter rotating bus 110. This bus is referred to as the interprocessor message transport (IMT) bus.
Each module illustrated in FIG. 1 may include an application processor and a communications processor. The application processor associated with each module performs a telecommunications function, such as routing for LIMs 102, converting between SS7 and IP for DCM 104, database services for DSMs 106, and maintenance and administration functions for MASPs 108. In addition, each processing module may include a communications processor for communicating with other processing modules via bus 110. The function of the communications processor is to send and receive messages to and from other processing modules over bus 110 and to perform card alignment.
When deploying multiple cards within the platform illustrated in FIG. 1, the alignment process enables each card to discover other cards that are present on IMT bus 110 and enables the card to establish a communications path with those cards via IMT bus 110. Such a communications path is referred to herein as an IMT virtual circuit (IVC). The alignment process may occur when a card that has been disconnected from IMT bus 110 for any reason is reconnected to IMT bus 110 or when a new card is added to IMT bus 110. Alignment may occur continuously to establish communications between existing cards and new cards as new cards are connected to IMT bus 110.
In current IMT implementations, IMT virtual circuits managed by a given communications processor use the same set of link level communications protocol parameters, regardless of the type of card on the other end of the IVC. In order to upgrade the link level communications capabilities of any card in the system, all cards must be configured to include the same upgrade. This restriction prevents the introduction of changes which might be beneficial for certain card-type pairings, but which should not be used for other card-type pairings.